1. Field of the Invention
The present invention relates to a receiver that has a multipath equalizer.
2. Description of the Related Art
As one of forms of FM broadcasting, there is broadcasting that broadcasts the same program at the same frequencies in order to efficiently use frequency resources. Now, A station and B station are assumed to carry out FM broadcasting at the same frequency, and an FM receiver is assumed to be located in the vicinity of A station and receive a signal from A station at a strong level. In this case, the FM receiver operates in a manner receiving and reproducing a signal from A station based on a principle of FM modulation. When the FM receiver is located in the vicinity of B station, the FM receiver operates in a manner receiving and reproducing a signal from B station. As described above, there is a nature (called a nature phenomenon) of receiving, reproducing, and outputting a signal with a stronger receiving level in FM demodulation.
Since FM modulation is a modulation system that superimposes information on frequencies of a signal, there is a certain degree of resistance to fading. However, under a multipath fading environment having a long delay time, performance deterioration called multipath distortion occurs. As a technique to reduce the multipath distortion, there is multipath equalizer. The multipath equalizer is a technique that controls a weight for equalizer corresponding to a propagation path in an adaptive manner to reduce multipath distortion.
The multipath equalizer enables provision of an FM receiver with reduced multipath distortion and excellent sound quality. On the other hand, there is a side effect that the capture phenomenon described above is intensified. For example, consideration will be made with respect to a case where there are two stations, A station and B station, that exist adjacent to each other, and an FM receiver equipped in a moving station such as a car moves from a location a in the vicinity of A station to a location b in the vicinity of B station. In this case, at the location a, a receiving level of a signal from A station is high and a receiving level of a signal from B station is low. When the FM receiver is moved near the location b, this relationship is reversed in due time.
The FM receiver not equipped with an equalizer that carries out multipath equalization as described above receives and reproduces a signal from A station while a receiving level of a signal from A station in the vicinity of the location a is high, and receives and reproduces a signal from B station when a receiving level of a signal from B station becomes high after moving to the location b. That is, the FM receiver receives and reproduces a signal from a broadcasting station with a high receiving level at all times.
In contrast, in an FM receiver equipped with an equalizer, a phenomenon, in which a signal from A station is received and reproduced even when a receiving level of a signal from B station becomes high by moving to the location b, occurs. This phenomenon is generated due to a reason that once the FM receiver acquires a signal from A station when the FM receiver is located in the vicinity of A station, an effect of such acquisition continues even when a receiving level of a signal from B station becomes high.
JP-A 2006-238295 (KOKAI) discloses a technique that initializes and restarts adapting processing with respect to a receiving signal when receiving of a signal other than a signal from a desired station is determined to be detected based on a program identity (PI) which is obtained as a result of decoding carried out by a radio data system (RDS) decoder. By this technique, possibility of capturing a signal from a desired station can be increased.
In the system described in the above document, even when there are a plurality of broadcasting stations that broadcasts the same program at the same frequencies, only a signal from a desired station that is determined in advance is received. Accordingly, a signal from a broadcasting station with high receiving level cannot be always received and reproduced.